In the assembly of various types of electronic apparatus, such as communication transmission equipment, a plurality of printed circuit boards are plugged into connector plugs of a backplane assembly for interconnection of the boards to other electronic apparatus. In order to facilitate the insertion of plug-in portions of the boards into the connector plugs, guide shelves are provided for supporting the boards and aligning the boards with the connector plugs. In this regard, upper guideways of one guide shelf cooperate with lower guideways of an adjacent guide shelf to slidably receive lower and upper edges, respectively, of the printed circuit boards, for this purpose.
In the past, the guide shelves, which frequently are of molded die cast construction, have been mounted in a transmission bay frame in various arrangements. For example, one or more sets of the guide shelves merely have been secured between opposed end or side support plates by mounting screws extended through clearance holes in the side support plates and then screw-threaded into the guide shelves. The side support plates subsequently are secured, by suitable integral brackets, to vertical frame members of the communications bay frame. In the alternative, the sets of guide shelves may be secured directly to the vertical frame members of the communications bay frame by mounting screws. In either instance, backplane assemblies, each comprising a backplane member having connector plugs mounted thereon, subsequently are secured to respective pairs of mounted guide shelves to form an assembly for receiving and connecting the printed circuit boards to respective ones of the connector plugs.
However, with the introduction of high density printed circuit boards and associated high density connector plugs, edge contact pads on the circuit boards and terminals on the connector plugs may be spaced extremely close together, such as on the order of 0.100". Accordingly, greater accuracy in the location of the guideshelves and the backplane assemblies with respect to one another is required to insure that the edge contact pads of the printed circuit boards mate properly with their respective terminals in the connector plugs. In this regard, the use of integrally formed locating bosses on the guide shelves and of conforming boss-receiving apertures in the side support plates, has been found to be not entirely suitable for this purpose. More specifically, it has been found that during the casting of the guide shelves, one or more of the bosses occasionally may be formed slightly oversize several thousandths of an inch, as a result of the casting apparatus opening slightly during the casting operation. Accordingly, when an attempt is made to assemble the guide shelf to a respective one of the side support plates, it is extremely difficult, and at times impossible, to force the oversize bosses into their associated boss-receiving apertures in the side support plates.
Accordingly, a purpose of this invention is to provide a new and improved substrate support module in which guide shelves and backplane assemblies can be readily and accurately assembled into the module.